Device for and method of generating ozone

ABSTRACT

The present invention can provide an electrode member having a substrate member and a coating member. The substrate member can be made of a material selected from the group consisting of titanium, gold coated titanium and other inert conducting materials. The coating member can have a tin dioxide modified by antimony. The electrode member of the present invention can be used for direct generation of ozone in water or through water into a gaseous state.

RELATED PATENT APPLICATION

This patent application claims the benefit of U.S. ProvisionalApplication No. 60/447,948 filed Nov. 10, 2003.

FIELD OF THE INVENTION

The present invention relates generally to the generation of ozone. Inparticular, the present invention relates to an electrode material forgenerating ozone and a method of making the electrode material. Thepresent invention also relates to a high concentration of dissolvedozone and an ozone generation system for generating the same.

BACKGROUND OF THE INVENTION

Ozone has many industrial applications, such as destructing organic andinorganic contaminants in wastewater and sludge, householdsdisinfectants, swimming pools and hospitals, bleaching paper, etchingsemiconductor surfaces, decolorizing water, removing odor from clothing,and terminating pests. [See, Bruno Langlais, David A. Reckhow, DeborahR. Brink; Ozone in Water Treatment application and Engineering, LewisPublishers, INC. 1991, and references discussed therein.] Chlorinationis commonly used in similar applications but will leave undesirablechlorinated organic residues. Ozone on the other hand will selfdisappear in time and leaves fewer potentially harmful residues.

There are two main types of technologies to produce ozone. The firsttype of technology involves the corona discharge process, wherein ozoneis formed from oxygen in air by the corona discharge in an intense andhigh frequency alternating electric field [see, U.S. Pat. Nos.5,882,609; 5,939,030; 6,022,456; 6,153,151]. This type of technologygives low ozone concentration (about 2% to oxygen) and can produceharmful nitrogen oxides. The generation of ozone is in the gas phase andto obtain dissolved ozone, the gaseous ozone is brought into contactwith water and the amount of dissolved ozone is limited by the gas phaseozone concentration and the solubility.

The other type of ozone generation technology is an electrochemical andelectrolytic process, wherein water is decomposed to ozone by passing anelectric current through the electrodes immersed in an aqueouselectrolyte. Since ozone is generated directly in water, this processcan provide high concentration of ozone at a high current efficiency.Over 35% current efficiency has been reported at low temperatures of−30° C. to −65° C. [see, P. C. Foller, C. W. Tobias, J. Electrochem.Soc., 129 (1982), 506]. A recent report discussed a 3.0 mg/lconcentration of dissolved ozone [see, Tatapudi and Fenton, J.Electrochem. Soc., 140 (1993) 3527].

In aqueous solution, ozone is formed by electrolytic decomposition ofwater, represented by following equations:

3H₂O→O₃+6H⁺+6^(e−), E°=1.51 V,  (1) and

H₂O+O₂→O₃+2H⁺+2^(e−), E°=2.07 V.  (2)

The oxygen evolution reaction, a competitive process at a lowerpotential should occur more easily according to the following equation:

2H₂O→O₂+4H⁺+4^(e−), E°=1.23 V.  (3)

Typically, mostly oxygen and very little ozone is generated uponelectrolysis. Some devices aim for co-generation of oxygen and ozone byelectrolysis of water [see U.S. Pat. No. 5,993,618]. Platinum, alpha andbeta-PbO₂, Pd, Au, RuO₂-DSA's, and glassy carbon in differentelectrolytes have been considered and tested for ozone generation. Gold,RuO₂-DSA's, and glassy carbon have been found to have very low currentefficiency (less than 1%). Platinum shows a current efficiency from 6.5%to 35% at very low temperature of about −50° C. However the currentefficiency falls to around 0.5% at room temperature. Obtaining a highcurrent efficiency at a low temperature will require additionalequipment and energy cost to make existing systems less efficient andconvenient. PbO₂ electrodes can produce ozone at a current efficiency of13% at room temperature [see, U.S. Pat. No. 5,407,550]. With potassiumfluoride electrolyte, a 16% current efficiency at 30° C. has beenreported [see, Ten-Chin Wen and Chia-Chin Chang, J. ElectrochemicalSociety, 140, (1993) 2764]. However, such a process releases toxic Pbions into electrolyte solution.

U.S. Pat. Nos. 5,972,196; 5,989,407; 6,287,431 B1; 6,365,026 B1; and6,576,096 B1 disclose dissolved ozone generators using integratedelectrochemical cells. Electrodes that improve dissolved ozoneconcentration and current efficiency at room temperature are needed incommercial applications.

Tin dioxide, a non-toxic semiconductor, has been studied forapplications in sensors, batteries and oxygen evolution. Low currentefficiency and instability had been reported when such tin dioxide wasused for electrochemically generating ozone in concentrated sulfuricacid.

SUMMARY OF THE INVENTION

The present invention can provide an electrode member. The electrodemember can comprise a substrate member and a coating member. Thesubstrate member can be made of a material selected from the groupconsisting of titanium, gold coated titanium and other inert conductingmaterials. The coating member can comprise a tin dioxide modified byantimony. The particles of Sn and Sb can be in an atomic ratio fromabout 6:1 to about 10:1. Additionally or alternatively, a predeterminedamount of nickel can be added in the coating member. The coating membercan comprise particles from about 3 nm to about 5 nm in size.

The electrode member of the present invention can be used for directgeneration of ozone in water or through water into a gaseous state. Thewater can contain an electrolyte selected from the group consisting ofHClO₄, H₂SO₄ and H₃PO₄. The electrolyte can be present in aconcentration from about 0.01 M to about 0.5 M.

The present invention can also provide an ozone generation systemcomprising such an electrode member to generate ozone efficiently. Theozone generation system can comprise a solid polymer electrolyte, suchas Nafion. Alternative, ozone can be generated in pure water, withoutthe need of dissolved ions. The present invention can further provide adissolved ozone with a high concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of the present invention will be betterunderstood in conjunction with the accompanying drawings as follows:

FIG. 1 is a SEM surface morphology of an antimony doped SnO₂ electrodemember of the present invention;

FIG. 2 is a graph illustrating the aqueous ozone concentration as afunction of electric charge; and

FIG. 3 is a graph illustrating the instantaneous aqueous ozoneconcentration as a function of scan potential.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary electrode members and ozone generation systems embodying theprinciples of the present invention will now be described in detail.

The present invention can provide an electrode member. The electrodemember can comprise a substrate member and a coating member. In oneexemplary embodiment, the substrate member can be made of a materialselected from the group consisting of titanium, gold coated titanium andother inert conducting materials. For example, the substrate member ismade of titanium. In an exemplary embodiment, the substrate member canbe made of titanium and be spot-welded with a titanium wire. It will beappreciated that other materials of the substrate member are also withinthe scope of the present invention.

The coating member can be made of various materials and in variousforms. In one exemplary embodiment, the coating member can comprise atin dioxide. In an exemplary embodiment, the coating member can comprisean antimony modified tin dioxide film. For example, the coating membercan comprise SnCl₄□5H₂O and SbCl₃. In another exemplary embodiment, thecoating member can comprise a predetermined amount of nickel. In oneexemplary embodiment, the coating member can be in the form of asolution, before being affixed onto the substrate member. It will beappreciated that other materials and forms of the coating member arealso within the scope of the present invention.

In another exemplary embodiment, the coating member can compriseparticles of various sizes. For example, the coating member can compriseconnected particles of less than 5 nm in size. In one exemplaryembodiment, the connected particles can be from about 3 nm to about 5 nmin size. It will be appreciated that other sizes of the particles arealso within the scope of the present invention.

In a further exemplary embodiment, the coating member can compriseparticles of various ratios. In an exemplary embodiment, the particlesof oxides of Sn and Sb can have an atomic ratio of more than 6:1. Inanother exemplary embodiment, the particles of oxides of Sn and Sbparticles can have an atomic ratio of less than 10:1. In a furtherexemplary embodiment, the particles of Sb and Ni can be in an atomicratio of more than 4:1. In a still further exemplary embodiment, theparticles of Sb and Ni can be in an atomic raitio of less than 10:1. Itwill be appreciated that other ratios of the particles are also withinthe scope of the present invention.

In a preferred embodiment, the electrode member can be made of titaniumand coated with antimony doped tin dioxide with surface morphologycomposed of 3 to 5 nm particles connected and covering substantially theentire surface. In another preferred embodiment, the particles compriseSn and Sb in a ratio from about 6:1 to about 10:1. In a furtherpreferred embodiment, the atomic ratio of Sn:Sb:Ni can be about 500:8:1.The electrode member can yield high concentration of dissolved ozone atroom temperature with high current efficiency.

The electrode member can be prepared in various manners. In oneexemplary embodiment, a substrate member and a coating member of variousforms can be provided, which can be similar to those described above. Ifdesired, the substrate member can be treated or otherwise prepared byvarious conventional methods. For example, the substrate member can beetch cleaned in an acid solution and then rinsed and dried. It will beappreciated that other methods of treating or preparing the substratemember are also within the scope of the present invention.

The substrate member can be affixed with the coating member in variousmanners. For example, the substrate member can be sprayed with, dippedinto, or otherwise coated with the coating member. In an exemplaryembodiment, the coating member can be sprayed with solution of 2.5 gSnCl₄□5H₂O and 0.025 g SbCl₃ in 25 ml of ethanol-HCl mixture. In anexemplary embodiment, the coating member can be dipped into 25 mlethanol-HCl mixture solution of 2.75 g SnCl₄□5H₂O and 0.025 g SbCl₃. Itwill be appreciated that other methods of affixing the coating member tothe substrate member are also within the scope of the present invention.

The coated substrate member can then be heat treated in various manners.In one exemplary embodiment, the coated substrate member can be dried,such as at a temperature of about 100° C. for about ten minutes. Inanother exemplary embodiment, the coated substrate member can becalcined, such as at a temperature of about 520° C. in air for 5 mins.The above coating, drying, and calcining steps can be repeated. In anexemplary embodiment, these steps can be repeat for 12 times. In anotherexemplary embodiment, these steps can be repeat for 20 times. It will beappreciated that other heating methods including heating temperaturesand/or time periods are also within the scope of the present invention.

The present invention can also provide a high concentration ozonematerial. In one exemplary embodiment, approximately 35 mg/l aqueousozone can be provided with over 15% current efficiency. In an exemplaryembodiment, the 15% current efficiency only accounts for the dissolvedozone. In a preferred embodiment, such an aqueous ozone can be generatedin a 6 min constant potential polarization at low electrolyteconcentration at room temperate. In another exemplary embodiment, asignificant amount of gaseous ozone can be generated and distinctlydetected by the normal smell test. The measurement of gaseous ozone canshow a much high current efficiency. The solution with dissolved ozonecan decolorize a dye such as indigo instantly. High overpotential ofoxygen evolution was observed in cyclic voltammetry.

Various systems can be used to generate a high concentration ozonematerial. In one exemplary embodiment of the present invention, an ozonegeneration system can be in the form of an electrochemical system forgenerating the high concentration ozone material. In an exemplaryembodiment, the electrochemical system can comprise a cell member forcontaining an electrolyte material of various forms. For example, theelectrolyte material can comprise SnCl₄□5H₂O and SbCl₃ in an ethanol-HClmixture. In another exemplary embodiment, ozone can be generated in purewater, without the need of dissolved ions. It will be appreciated thatvarious other types of ozone generation systems are also within thescope of the present invention.

In one exemplary embodiment, the ozone generation system can adopt theelectrode member of the present invention for generating the highconcentration ozone. In an exemplary embodiment, the electrode membercan be used as a working electrode. For example, the electrode membercan be used as an anode member in a electrochemical system. In anotherexemplary embodiment, the electrode member can be positioned on thebottom of the cell member. In a further exemplary embodiment, a constantpotential can be applied to the electrode member, such as at roomtemperature. The constant potential can range from 1.5V to 3V withrespect to a reference electrode. In an exemplary embodiment, theconstant potential can be about 2.5V. It will be appreciated thatvarious other forms of the ozone generation system are also within thescope of the present invention.

The present invention will now be describe in further detail inconnection with the various Examples below.

EXAMPLE 1

A 0.8×0.8×0.05 cm³ titanium (Ti) sheet member spot-welded with a 1 mmdia. titanium wire was first etch cleaned in a 10% boiled oxalic acidsolution for 1 hour, then rinsed with distilled water and dried. Anantimony doped SnO₂ electrode member was prepared by a spray pyrolysistechnique on the pretreated Ti substrate member. The spray solution was2.5 g SnCl₄□5H₂O and 0.025 g SbCl₃ in 25 ml of ethanol-HCl mixture.After drying the sprayed substrate member at 100° C. for 10 min, thesubstrate member was calcined at 520° C. in air for about 5 min. Thistreatment was repeated 12 times. The resulting electrode member showed acompact smooth surface morphology with connected particles having adiameter of about 3 to 5 nm (see FIG. 1). The atomic ratio of Sn to Sbin the film is about 7:1 by ICP analysis.

Ozone was generated in a cell with 3 ml 0.1 M HClO₄. The prepared dopedSnO₂ electrode member was used as a working electrode member positionedon the bottom of the cell. A 0.8 cm² platinum sheet was used as acounter electrode member positioned at the up-region of the electrolyte.An Ag/AgCl member was used as a reference electrode member andpositioned closer to the working electrode member. A constant potential(vs. the Ag/AgCl member) of 2.5V was applied to the working electrodemember at room temperature. About 35 g/l of ozone dissolved in theelectrolyte was generated in about 6 min. (see FIG. 2). The ozoneconcentration was determined by UV absorption as well as a standardindigo method.

EXAMPLE 2

An antimony doped SnO₂ electrode was prepared by dipping a Ti substratewith the same area as described in Example 1 into 25 ml ethanol-HClmixture solution of 2.75 g SnCl₄□5H₂O and 0.025 g SbCl₃. Before dryingthe dipped the Ti substrate at 100° C., excess solution on the substratesurface was removed to leave a thin uniform liquid layer on thesubstrate surface. The substrate member was calcined at about 520° C.The time periods for drying and calcining were the same as in Example 1.The above process was repeated 30 times. The surface morphology of theresulting electrode was similar to that shown in FIG. 1. The ratio of Snto Sb in the film is about 10:1 by ICP analysis.

Ozone was generated using the same system as in Example 1. SnO₂electrode was performed by cyclic voltammetry in a potential rangingfrom 1.5 V to 3 V (vs. the Ag/AgCl member) at the scan rate of 1 mV/s atroom temperature. FIG. 3 shows the ozone generated against scanpotential.

EXAMPLE 3

A solution of 1 molar SnCl₄□5H₂O, 0.016 molar SbCl₃, and 0.002 molarNiCl₂□6H2O in absolute ethanol was used as the coating solution. Atitanium sheet can be coated in the same manner by dip coating andpyrolysis, as described in Example 1. The coating and pyrolysis wasrepeated 7 times. The resulting Ni—Sb doped SnO₂ coated electrode memberwas tested to give better ozone generation. The current efficiency canreached more than 25% at room temperature using 0.1 molar perchloricacid electrolyte and with applied electric potential of 2.2 V (vs. theAg/AgCl member). The ozone generation and measurement was the same asdescribed in Example 1.

It will be appreciated that the various features described herein may beused singly or in any combination thereof. Therefore, the presentinvention is not limited to only the embodiments specifically describedherein. While the foregoing description and drawings represent apreferred embodiment of the present invention, it will be understoodthat various additions, modifications, and substitutions may be madetherein without departing from the spirit of the present invention. Inparticular, it will be clear to those skilled in the art that thepresent invention may be embodied in other specific forms, structures,arrangements, proportions, and with other elements, materials, andcomponents, without departing from the spirit or essentialcharacteristics thereof. One skilled in the art will appreciate that theinvention may be used with many modifications of structure, arrangement,proportions, materials, and components and otherwise, used in thepractice of the invention, which are particularly adapted to specificenvironments and operative requirements without departing from theprinciples of the present invention. The presently disclosed embodimentsare therefore to be considered in all respects as illustrative and notrestrictive.

1. A method of generating ozone using an electrochemical ozonegeneration system, the ozone generation system including an electrodemember having a substrate member and an antimony modified tin dioxidecoating member that further comprises nickel, the method comprising:providing the electrode member for use as a working electrode; applyinga constant potential to the electrode member; and generating ozone froman electrolyte.
 2. The method of claim 1, wherein providing theelectrode member comprises: providing a substrate member comprising aninert conductive material; affixing a coating member comprising antimonymodified tin dioxide and further comprising nickel to the substratemember to produce the electrode member; drying the electrode member;calcining the electrode member; and repeating the drying and calciningsteps a predetermined number of times.
 3. The method of claim 2 whereinthe coating member comprises SnCl₄-5H₂O, SbCl₃, NiCl₂-6H₂O in absoluteethanol.
 4. The method of claim 2, wherein affixing a coating member tothe substrate member comprises spraying a solution of SnCl₄-5H₂O SbCl₃and a nickel compound in an ethanol-HCl mixture onto the substratemember to produce a surface morphology of approximately 3 to 5 nmconnected particles covering substantially all of the substrate member.5. The method of claim 2, wherein affixing a coating member to thesubstrate member comprises dipping the substrate member into a solutionof SnCl₄-5H₂O SbCl₃ and a nickel compound in an ethanol-HCl mixture toproduce a surface morphology of approximately 3 to 5 nm connectedparticles covering substantially all of the substrate member.
 6. Themethod of claim 2, wherein drying the electrode member comprises heatingthe electrode member at about 100° C. for about 10 minutes.
 7. Themethod of claim 2, wherein calcining the electrode member comprisescalcining the electrode member at a temperature of about 520° C. in airfor about 5 minutes.
 8. The method of claim 2, wherein repeating thedrying and calcining steps a predetermined number of times comprisesrepeating the drying and calcining steps between 12 and 30 times.
 9. Themethod of claim 1, wherein applying a constant potential to theelectrode member comprises applying between approximate 1.5V to 3V ofconstant potential at room temperature to the electrode member.
 10. Themethod of claim 1, wherein generating ozone from an electrolytecomprises generating approximately 35 mg/l aqueous ozone.